1. Field of the Invention
The present invention relates to a quantization error correcting method and device, and audio information decoding method and device including the quantization error correcting method and device. More specifically, the present invention relates to a method and a device for correcting quantization error generated during decoding compressive-encoded audio information.
2. Description of Related Art
In order to record audio information (including voice information and other sound information, hereinafter used in the same meaning) of long playback time onto an information storage medium (e.g., an optical disc) having limited recording capacity, audio information is subjected to compressive-encoding (generally also referred to as xe2x80x9chigh-efficiency encodingxe2x80x9d) before it is recorded on an information storage medium.
As a compressive-encoding method for audio information to be recorded, there is known a method which divides audio information into a plurality of frequency bands, and then encodes the audio information by the frequency band unit using appropriately allocated bit numbers (different from each other in different frequency bands). Specifically, according to a digital compression method called xe2x80x9cSub-band encodingxe2x80x9d, an audio signal including audio information of time domain is divided into blocks of some samples, and a time-frequency conversion using orthogonal base, such as Modified Discrete Cosine Transform (MDCT), is applied to each block to obtain conversion coefficient in frequency domain. Then, the signal is frequency-divided by a digital compression method for quantizing by the conversion coefficient unit (called xe2x80x9cconversion encoding method), and/or a filter bank including Band Pass Filters, High Pass Filters and Low Pass Filters. Then, the resultant signal is decimated according to the divided frequency band widths, and then quantized by the frequency band unit.
In the bit allocation (i.e., step of allocating bit number), in consideration of so-called masking effect, small bit number is allocated to a frequency band generally inaudible to human being and large bit number is allocated to a frequency band audible to human being. Thus, compressive-encoding is performed with efficiently reducing total information amount of audio information. It is noted that the masking effect is that, if there are sound of high sound pressure and low sound pressure in near frequency band to each other, human being is hardly recognize sound of low sound pressure level (especially if sound of low sound pressure has higher frequency than that of the sound of high sound pressure).
According to the compressive-encoding method described above, the information amount is efficiently reduced with suppressing the deterioration of sound quality in consideration of audible characteristic of human being, thereby effectively compressive-encoding audio information.
However, there is a problem that the decoding accuracy may be degraded for audio information encoded with small bit number. Namely, for the audio information encoded with small bit number, the difference between digital value before the encoding and after the decoding increases.
In view of the recent trend which regards high sound quality as a significant factor, it is desirable that even audio information inaudible due to the masking effect is reproduced with high fidelity in order to achieve high accuracy reproduction of whole audio information.
It is an object of the present invention to provide a quantization error correction method and device capable of improving decoding accuracy of audio information encoded with small bit number.
It is another object of the present invention to provide audio information decoding method and device which take advantage of the above improved decoding accuracy to achieve high accuracy decoding of whole audio information.
According to one aspect of the present invention, there is provided a quantization error correcting device for correcting quantization error included in audio information at the time of decoding, the audio information being divided into a plurality of frequency bands and compressive-encoded for each frequency band with bit allocation determined based on audible frequency characteristic, the device including: a detecting unit for detecting, based on bit allocation information indicating bit allocation and encoded values of the compressive-encoded audio information, a range of quantization error indicating a range in which audio information value before compressive-encoding corresponding to the encoded value exists; and an outputting unit for outputting a decoded value corresponding to one of the encoded values based on the detected range of quantization error and the ranges of quantization errors of other correlated ones of the encoded values.
According to the same aspect of the present invention, there is provided a quantization error correcting method for correcting quantization error included in audio information at the time of decoding, the audio information being divided into a plurality of frequency bands and compressive-encoded for each frequency band with bit allocation determined based on audible frequency characteristic, the method including the steps of: detecting, based on bit allocation information indicating bit allocation and encoded values of the compressive-encoded audio information, a range of quantization error indicating a range in which audio information value before compressive-encoding corresponding to the encoded value exists; and outputting a decoded value corresponding to one of the encoded values based on the detected range of quantization error and the ranges of quantization errors of other correlated ones of the encoded values.
In accordance with the above device or method, the decoded value corresponding to one of the encoded values is outputted based on the detected range of quantization error and the ranges of quantization errors of other correlated ones of the encoded values. Therefore, the quantization error in the audio information of the frequency band which is compressive-encoded with small bit number according to the bit allocation at the time of the encoding may be corrected, and the decoding accuracy may be improved.
The outputting unit or step may correct the quantization error corresponding to the one of the encoded value using Least Mean Square method based on the detected range of the quantization error and the ranges of the quantization errors of the other correlated ones of the encoded values, and output the decoded value. Thus, the decoded value may be outputted highly accurately by the LMS method.
The other correlated ones of the encoded value may include the encoded values which are compressive-encoded in the frequency bands neighboring to the frequency band in which the one of the encoded value is obtained. By this, the quantization error may be corrected by simple processing.
According to another aspect of the present invention, there is provided a quantization error correcting device for correcting quantization error included in audio information at the time of decoding, the audio information being divided into a plurality of frequency bands and compressive-encoded for each frequency band with bit allocation determined based on audible frequency characteristic, the device including: a memory for storing correction values for correcting the encoded values for each frequency band, the correction values being calculated based on, at least, an error between the encoded value of the compressive-encoded audio information and audio information value before compressive-encoding, and a level of the encoded value in other correlated ones of the encode values; and an outputting unit for reading out the correction value from the memory based on the bit allocation information indicating the bit allocation and the encoded value, and for outputting decoded value corresponding to the encoded value for each frequency band based on the correction value read out from the memory and the encoded value.
According to the same aspect of the present invention, there is provided a quantization error correcting method for correcting quantization error included in audio information at the time of decoding, the audio information being divided into a plurality of frequency bands and compressive-encoded for each frequency band with bit allocation determined based on audible frequency characteristic, the method including the steps of: storing correction values for correcting the encoded values for each frequency band into a memory, the correction values being calculated based on, at least, an error between the encoded value of the compressive-encoded audio information and audio information value before compressive-encoding, and a level of the encoded value in other correlated ones of the encode values; and reading out the correction value from the memory based on the bit allocation information indicating the bit allocation and the encoded value, and for outputting decoded value corresponding to the encoded value for each frequency band based on the correction value read out from the memory and the encoded value.
In accordance with the device or method, the correction value is read out from the memory based on the bit allocation information and the encoded value, and the decoded value corresponding to the encoded value is outputted for each frequency band based on the correction value read out from the memory and the encoded value. Therefore, the quantization error in the audio information of the frequency band which is compressive-encoded with small bit number according to the bit allocation at the time of the encoding may be corrected, and the decoding accuracy may be improved.
The compressive-encoding of the audio information may be conversion encoding or sub-band encoding for each of the frequency bands.
According still another aspect of the present invention, there is provided an audio information decoding device including: the quantization error correction device described above; and a decoding unit for applying decoding processing corresponding to the compressive-encoding of the audio information onto the outputted decoded value and for outputting decoding result.
According to the same aspect of the present invention, there is provided an audio information decoding method including: the quantization error correction method described above; and a step of applying decoding processing corresponding to the compressive-encoding of the audio information onto the outputted decoded value and outputting decoding result.
In accordance with the device or method, it is possible to generate decoded value in which quantization error in the audio information of the frequency band compressive-encoded with small bit number is corrected, and hence the decoding accuracy of the audio information may be improved.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.